File:Telephones and telegraphs- 1902 - (and Municipal electric fire alarm and police patrol systems) (1906) (14569654908).jpg

Identifier: cu31924022817674 (find matches)
Title: Telephones and telegraphs: 1902 : (and Municipal electric fire alarm and police patrol systems)
Year: 1906 (1900s)
Authors: United States. Bureau of the Census Steuart, William Mott, 1861- Martin, Thomas Commerford, 1856-1924 Abbott, Arthur Vaughan, 1854- Mayer, William
Subjects: Telephone Telegraph Fire alarms
Publisher: Washington : Govt. Print. Off.
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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and an alternating current is produced. Thusthis machine is merely a magneto dynamo on a suffi-ciently small scale to be easily actuated by hand. A magneto bell is shown in Fig. 3 on plate facingpage 36. This bell consists of a frame which supportsa pair of gongs, a pair of magnet spools, a U-shapedpermanent magnet, and an armature pivoted in frontof the poles of the electro-magnets, carrying a clapperso arranged that when the armature swings, theclapper will strike against the edges of the gongs. The magneto call possesses the advantage that itcontains no contacts to corrode and requires no bat-tery maintenance, while the generators can be easilybuilt to give sufficient pressure or voltage of currentto operate the longest line. Protection, of substation.—The telephone line oftenis accidentally crossed with other conductors carryingdangerous potentials or large currents and the aerialcircuit is sometimes struck by lightning. Either con-tingency may damage the substation, expose the
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